1. Field of the Invention
This invention relates to a method of separating .alpha.-crystals of phenylalanine.
2. Description of the Prior Art
Phenylalanine is an essential amino acid (a vital nutrient) and is also a substance of industrial importance useful as a raw material for the production of L-aspartyl-L-phenylalanine methyl ester, a sweetener.
Phenylalanine may be obtained by isolation from a hydrolyzate of protein, such as defatted soybeans, by fermentation or by organic synthesis; and crystallization is generally adopted as the method of purification in any of these processes. Optically active phenylalanine exists as .alpha.-crystals or .beta.-crystals, in which the .alpha.-crystals are in the form of plates or flakes, while the .beta.-crystals are in the form of fine needles. Hence, crystallization as the .alpha.-crystal is better in the case of isolation, and gives high-quality products with less mother liquor left attached.
Phenylalanine exists in the form of .alpha.-crystals at a temperature higher than a specific level (normal transition point temperature) and in the form of .beta.-crystals at a temperature lower than the normal transition point temperature. The normal transition point temperature of phenylalanine is about 37.degree. C. in aqueous systems and varies in some degree depending on the crystallization system. The transition point in a specific crystallization system can be easily measured by investigation of the crystals separated from said crystallization system, such as by observation under a microscope or X-ray powder diffractometry. It was known that the normal transition point temperature generally lowers by addition of an organic solvent, but no such phenomenon was known with aqueous systems.
Thus, a need exists for the obtention of crystals of phenylalanine in the .alpha.-crystal form at temperatures below the normal transition point temperature.